1. Field of the invention
The present invention relates to a soundproof material for vehicle to keep a room interior of a vehicle such as an automobile silent, and more specifically relates to a soundproof material for vehicle with an enhanced soundproof property and an enhanced productivity.
2. Description of the Related Art
Not only a soundproof property but also accuracy improvement and a thinner-wall structure have been required for a soundproof material for vehicle due to a necessity of making a vehicle room interior more spacious. As a matter of course, it has been required at the same time to save production processes and production time. Accordingly, a soundproof material for vehicle has been generally produced by laminating a sound absorbing material and a sound insulating material and then molding them by a pressing machine in order to meet requirements of solving a spacious restriction, with ensuring sound absorbing and sound insulating properties, and saving production processes at the same time. The sound absorbing material and the sound insulating material can be bonded to each other, for example, by a method of using a melted thermoplastic resin, namely a hot-melt, between them and cold pressing them just after melting them.
Japanese Patent Laid-Open No. 2005-227747 discloses an invention of a sound insulator having an object of raising transmission loss in a medium to high frequency domain generally having less transmission loss. It has an object of improving sound absorption in a medium to high frequency domain to which frequency of human conversation pertains. It also has an object of ensuring sufficient sound absorption even in a thin-wall sound absorption layer of an actual odd-shaped product and an object of reducing the weight of a sound insulator.
However, conventional methods of compression molding and thin-wall structure with high soundproof property disclosed in Japanese Patent Laid-Open No. 2005-227747 are still insufficient, in some cases, to meet high requirements of product thickness and soundproof property. Additionally, if one of layers is to be compressed particularly relative to other layers, amount of compression and thickness of the compressed layer were limited.